I've had great luck with yellow hibiscus in my garden, and I think the key is to make sure they get plenty of sunlight and water. I water mine every other day, unless it's been raining, and I fertilize them once a month with a balanced fertilizer. Pruning is also important, I prune mine back after it finishes blooming to encourage new growth and prevent it from getting too leggy. You should also deadhead the flowers as they fade to encourage more blooms. I've found that with regular care, my yellow hibiscus produces tons of beautiful flowers all summer long.